In the invention of our parent application, we discovered that a deep, double-walled box can be blow molded from a single parison that is closed and draped downward over a core so that a leading portion, next to the core, becomes an inside wall of the box, and a succeeding portion, surrounding the core, becomes an outside wall of the box. We balloon the parison to a size larger than the core as we invert and drape the parison down over the core. Outer mold parts then close around the parison draped over the core, and the parison is blown in the cavity between the core and the outer mold parts to form a double-walled box that is unlimited in depth.
In making the invention of the parent application work, I discovered a way of pinching closed and holding a lower region of the parison in place at the top of the core so that the parison can be ballooned as it drapes down over the core and can be held reliably in place during the draping. My device for accomplishing this is built into a core and is simple, effective, and economical to facilitate parison draping in a blow molding machine.